1. Field of the Invention
The present invention relates to an image reading apparatus such as a scanner that reads an original document. The present invention also relates to an image forming apparatus equipped with such an image reading apparatus.
2. Description of Related Art
There are image reading apparatuses reading an original document and then outputting image data thereof. Image forming apparatuses such as copiers, multi-functional apparatuses, and facsimiles are equipped with an image reading apparatus for a copying or scanning purpose. Typically, the image reading apparatus includes a lamp that shines light on an original document, that guides the light reflected from the original document into an image sensor, and that then obtains image data. Despite the fact that the image reading apparatus needs such light emission from the lamp, that lamp may not emit the amount of light necessary for performing a reading operation or there may be nonuniformity in the amount of light (for example, in one case where the main power switch is turned off on a previous day and turned on at the start of working on the next day, and in another case where the image reading apparatus has been placed in a low temperature environment for a long period of time with its main power switch remaining off) for one reason that the lamp is not yet warmed up right after the main power switch is turned on or other reasons. That is, reading of an image cannot be performed immediately after the main power switch is turned on; thus, it is necessary to wait until the amount of light emitted from the lamp is stabilized.
The technology coping with the inconvenience of requiring much time before the amount of light emitted from the lamp is stabilized is disclosed in JP-A-2005-318067. More specifically, JP-A-2005-318067 discloses an image forming apparatus including: a cold cathode light source; means for regulating an amount of light emitted from the light source; driving means for driving an optical system in a sub-scanning direction; a plurality of image sensors each converting light into an electrical image signal; an A/D converter converting the image signal into a digital signal; means for transferring the image signal thus digitally converted to an external device; means for reading a peak value of the digitally converted image data; means for performing calibration every time an image reading operation is performed; means for performing the image reading operation using calibration data stored in a memory and the like, without performing the calibration every time; and means for switching between the means for performing the calibration every time the image reading operation is performed and the means for performing the image reading operation without performing the calibration every time, wherein when the cold cathode light source is unstable on being turned on, the means for performing the image reading operation without performing the calibration every time is not selectable. With this configuration, it was intended to provide a scanner capable of preventing the image reading operation from being performed while the cold cathode light source is unstable (see claim 1 and paragraph [0008] of JP-A-200-318067).
As described earlier, so that in an image reading apparatus, the amount of light emitted from a lamp incorporated therein reaches a desired level and is stabilized, that lamp needs to be preliminarily turned on for a certain period of time and to be warmed up. Now, a conventional example of controlling turning-on of a lamp when a main power switch is turned on will be described with reference to FIG. 9 (for a case where a cold cathode lamp is used for the lamp). FIG. 9 is a timing chart showing one example of an operation when a main power switch of a conventional image reading apparatus is turned on.
First, in the chart, the topmost line indicates, as an example, an output voltage value for a main power switch (power supply device) of a copier (in FIG. 9, the main power switch is turned on at timing A′). The second line indicates when a control board starts operating, the control board being responsible for controlling the image reading apparatus (in FIG. 9, the operating starts at timing B′). More specifically, when the main power source is turned on, the power supply device generates a voltage for operating the control board, the CPU starts operating, a control program is read from a memory, and the CPU of the control board executes that program; in this way, start-up processes are executed including setting-up of a CPU port and the like. Through these processes, the lamp is put under control to be turned on (at timing B′).
Conventionally, turning-on of the lamp is controlled by a control board, and as indicated by the third line in the chart, after the control board starts operating, a lamp control signal (remote signal) becomes High so that the lamp is warmed up (the signal being transmitted from the control board at timing C′ in FIG. 9). At that time, as indicated by the lowermost line in FIG. 9, a cold cathode lamp is turned on. After the illumination starts at the timing C′, the CPU and the like starts counting an illumination time, and the amount of light emitted from the cold cathode lamp reaches a desired level and is stabilized (at timing D′ in FIG. 9). When the cold cathode lamp becomes stable, automatic adjusting functions for the reading operation such as shading correction are performed (between D′ and E′). Thus, in the example shown in FIG. 9, the image reading apparatus can be used only when a time period A′-E′ (represented by a time TA in the figure) has elapsed after the main power switch is turned on.
Typically, the amount of light emitted from the lamp is not stabilized immediately (for example, in the case of a cold cathode lamp, it takes approximately several tens of seconds if it is cooled). A time before the control board starts operating added to a time before the amount of light emitted from the lamp is stabilized makes a user waiting time long. That is, the waiting time before the amount of light emitted from the lamp of the image reading apparatus is stabilized inconveniently prevents shortening of the time from when the main power switch is turned on until when the apparatus is ready for a reading operation or, for a case where the image reading apparatus is incorporated in an image forming apparatus, a time before a first copying can be performed (from turning-on of the main power switch to the first copying).
Certainly, with the scanner disclosed in JP-A-20050318067, reading of images with density problems or images with poor S/N ratios may be avoided in some cases (see paragraph [0006] of JP-A-2005-318067); however, what is attained by the technology disclosed therein is simply making the means for performing the image reading operation without performing the calibration every time unselectable; consequently, the reading operation is still permitted even when there is nonuniformity in the amount of light emitted from the lamp, with the adverse effect that image data thus obtained is basically of poor quality. Moreover, with respect to the above-identified inconveniences, the conventional technology is not intended to positively cope with reducing a user waiting time. In fact, so long as the amount of light emitted from a lamp is stabilized right after the main power switch is turned on, there is no need to practice the technology disclosed in JP-A-2005-318067.